The pathophysiology of delayed neuronal injury which occurs hours and even days following cerebral ischemia are poorly understood. It is now apparent that excitotoxicity and inflammation can operate concurrently in the progression of ischemic neurodegeneration. While extravasation of inflammatory cells from the periphery may contribute to neuronal damage, 'inflammatory' genes expressed in parenchymal cells of the CNS can also play a deleterious role. Results from numerous animal studies indicate that cyclooxygenase-2 (COX-2) is one of the genes most strongly induced following cerebral ischemia and/or direct excitotoxin injection. COX-2 has also been shown to be induced in neurons of human brain following a lethal cerebral insult. During the last/current grant period, our laboratory was the first to establish a direct link between NMDA-induced neuronal COX-2 induction/activity and neuronal cell death. This observation serves as the basis for the following proposal. The objectives of this following 5 yr research plan of study are 1) to fully elucidate the contribution of COX-2 activity to excitotoxicity in vivo using direct intrahippocampal injections of NMDA and a selective pharmacological approach to identify compounds which effectively prevent injury as well as to elucidate their therapeutic time window, 2) to determine the molecular mechanisms by which NMDA regulates COX-2 expression using state of art molecular biological approaches to identify the cis-elements and their respective trans-activating factors in the COX-2 promoter responsible for NMDA-induced COX-2 mRNA transcription as well as in the 3' UTR region which governs mRNA stability; and 3) to identify the enzymatic pathway for COX substrate liberation by employing chemical inhibitors, antisense oligonucleotides and knockout technology to test the interesting and specific hypothesis that cPLA2 mediates NMDA-stimulated arachidonic acid release. All three aims are devised to identify specific drugs as well as alternate sites for potential therapeutic intervention in the COX-2 transduction cascade leading to excitotoxic neuronal cell death.
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